1. Field of the Invention
This invention relates to techniques for utilizing magnetic bubble domains, and more particularly to novel techniques for moving these bubble domains without requiring magnetic fields having spatial gradients. 2. Description of the Prior Art
In the bubble domain art, many techniques are known for moving magnetic bubble domains. These techniques generally require the presence of active overlays, such as conductor overlays and magnetic element overlays. Conductor propagation occurs because currents in conductors provide localized magnetic field gradients which move the bubble domains.
Another type of bubble movement is the type known as "field access" propagation. These field access propagation techniques generally utilize a magnetic field in the plane of the magnetic medium, together with a magnetic overlay. The magnetic field interacts with the overlay to produce traveling localized magnetic fields so that spactial gradients exist along the direction the magnetic domains are to travel. For instance, a magnetic field in the plane of the magnetic medium can be used in combination with permalloy overlay patterns, which can have many shapes. Among these, the T-I bars, Y-I bars, and curved elements are well known.
Another field access technique for moving domains utilizes ion implanted regions in a magnetic material. Again, the in-plane magnetic field interacts with the ion implanted areas of the magnetic material to produce localized magnetic poles or charged walls for movement of the domains.
Still another type of bubble domain motion uses modulations of the bias field in combination with wedge shaped patterns of magnetic material. The bubble domain is made to expand and contract and will thereby be moved along from one triangular wedge to the next due to the asymmetry of wall motion produced by the triangular wedges. If the triangular wedges are not present, continuous bubble movement in a desired direction cannot be obtained.
In all but the last of these propagation schemes, spatial gradients in the magnetic field are used to provide forces for movement of bubble domains in the magnetic medium. In contrast with this, the present invention seeks to utilize magnetic fields which are spatially uniform. Further, the present invention seeks to move magnetic bubble domains without requiring over- or under-layers of the types previously described. That is, there is no need for "active" propagation elements which, in combination with applied magnetic fields, will move domains. By the term "active" a distinction is made with regard to "passive" overlays which can be used, for instance, merely as guiding structures for the bubble domains. Such guiding structures are not necessary for providing the forces for actual movement of the domains, but rather only channel their direction of movement. Thus, the present invention is characteized by movement of magnetic bubble domains using magnetic fields which have no spatial gradients and wherein no active overlays are required for bubble movement.
In the present invention, time varying magnetic fields are applied to the bubble domains in order to change (precess) their wall magnetization vector distribution which in turn provides a reaction force to move domains in a desired direction. In order that continual application of the time varying field will move the domains, the original state of wall magnetization vectors tends to be restored prior to each application of the time varying magnetic field. Thus, bubble motion occurs by altering wall magnetization distribution, restoring this distribution, and again altering the distribution, etc.
The present invention is distinguished from that shown in U.S. Pat. No. 3,876,994 where an in-plane field is used to affect the mobility of the magnetic bubble material. In that patent, conventional propagation structures are used to move the domains, and no reference is made to the principle of operation of the present invention. At the very minimum, propagation in accordance with that patent requires active propagation elements.
Since uniform magnetic fields are used in the present invention, the structures which provide these fields can be removed from close proximity to the magnetic bubble domain chip. This means that there is less disturbance to the magnetic chip and that the overall structure is easier to fabricate and consumes less heating on-chip. Of course, this eases packaging requirements.
Another advantage of the present invention is that no active overlays are required and hence the density of devices using the principles described herein are not lithography limited. By merely changing the direction of the magnetic field used for restoration of wall magnetization distribution, the domains can be made to move in different directions. Additionally, the magnitudes of the magnetic fields used to alter wall magnetization distribution can also be readily changed for propagation of different types of bubble domains.
Another advantage is that bubble domains having the same winding numbers can be discriminated using the practices of this invention. previously, such domains could not be discriminated from one another since they will deflect along the same angle in a spatial gradient magnetic field. The ability to discriminate bubbles in this manner means that additional techniques for coding information are provided.
Another advantage of the present invention is that the automotion effect described herein produces a large effect. Optimally, velocities in the range 10.sup.2 -10.sup.3 cm./sec. are possible. If desired, the applied magnetic fields used for movement of the domain can be spatially uniform fields which are sinusoidal, preferably at or close to a natural resonance frequency of the domain (typically 1-10.sup.2 MHz). In this case, the amplitude of the time varying field need only be somewhat greater than the coercive field in order to produce the maximum domain velocity. Thus, an efficient mechanism for domain movement is provided.
Accordingly, it is a primary object of the present invention to provide a new technique for movement of magnetic bubble domains.
It is another object of the present invention to provide a technique for moving magnetic bubble domains which does not utilize magnetic fields having spatial gradients.
It is still another object of the present invention to efficiently move magnetic bubble domains without requiring active overlay structures.
It is a further object of the present invention to utilize magnetic fields without spatial gradients for the movement of magnetic bubble domains at high velocities.
A still further object of the present invention is to provide magnetic bubble domain propagation by a technique which is not lithography-limited.
A further object of the present invention is to provide systems utilizing magnetic bubble domains for information storage, whose density is not limited by lithography.
Another object of the present invention is to provide improved techniques for discriminating magnetic bubble domains which have the same or different winding numbers.
Still another object of the present invention is to provide a technique for generation, propagation, and detection of magnetic bubble domains using magnetic fields having no spatial gradients.
Still another object of the present invention is to provide magnetic bubble domain manipulation using magnetic fields which are easily provided and in which the packaging of device structures is facilitated.
A further object of the present invention is to provide a technique for moving magnetic bubble domains using spatially uniform, time varying magnetic fields whose amplitudes are not excessively large.